1. Field of the Invention
This invention relates to a water dispersible granule formulation containing biocontrol agents for the reduction of aflatoxin contamination in food and feed commodities, in particular corn, and a method of preparing the formulation. The water dispersible granule formulation comprises biocontrol agents embedded in a granular matrix which is dispersible upon the addition of an aqueous solvent. The biocontrol agents are non-toxigenic and non-aflatoxigenic Aspergillus flavus strains which are capable of inhibiting colonization by aflatoxin-producing fungi and which are further capable of suppressing production of aflatoxin by the toxigenic fungi. The water dispersible granule formulation of the invention exhibits a high degree of stability under storage and field conditions.
2. Description of the Relevant Art
Many fungi produce secondary metabolites that are not necessary for their growth or reproduction. When toxic to humans or livestock, these metabolites are classified as mycotoxins. Four of the more important mycotoxin-producing fungal genera are Aspergillus, Fusarium, Penicillium, and Alternaria (Council for Agricultural Science and Technology [CAST]. 2003. Task Force Report 139, Ames, Iowa). These fungi produce mycotoxins that could adversely affect the quality and supply of various food and feed commodities including corn, cottonseed, cereal grains, peanuts, and tree nuts.
Mycotoxins are estimated to cost the United States and Canadian feed and livestock-industries an overall loss of five billion annually: aflatoxin, a class of mycotoxins produced by Aspergillus spp., is of the greatest concern (Robbens and Cardwell. 2005. In: Aflatoxin and Food Safety, Abbas, H. K (Ed.), CRC Press, Boca Raton, Fla., pp. 1-12) The two major mycotoxins prevalent as contaminants in food and feed produced by A. flavus are aflatoxins B1 and B2 (Payne, G. S. 1992. Critical Rev. Plant Sci. 10: 423-440). Aflatoxin B1 (AFB1) is regarded as the most potent and prevalent (International Agency for Research on Cancer-World Health Organization [IRAC-WHO]. 1993. In: IARC Monographs on tho Evaluation of Carcinogenic Risks to Humans, Lyon, France, pp. 56, 467-488). Incidences of contamination are most frequently linked to A. flavus (Diener et al. 1987. Ann. Rev. Phytopath. 25: 249-270). This fungus-is capable of growing over a wide temperature range, namely 10° C.-43° C. and a wide water activity range (0.82-0.998) (Food and Agriculture Organization of the United Nations/International Atomic Energy Agency [FAO/IAEA]. 2001. In: FAO Food and Nutrition Paper, FAO. Rome, Italy, pp. 73, 75-93). However, drought conditions, mechanical injury, or pest damage generally exacerbates preharvest aflatoxin contamination in corn.
The current maximum aflatoxin level permissible in human food and animal feed is 20 μg/kg (CAST, supra; van Egmond and Jonker. 2004. J. Toxicol.—Toxin Rev. 23: 273-293). Although mycotoxins on agricultural commodities are unavoidable, the level of these contaminants may be controlled with good agronomic practices. Several preharvest aflatoxin management strategies have been proposed (Betran and Isakeit. 2004. Agron. J. 96: 565-570) with varying degrees of success. One promising control strategy is biological control using non-toxigenic A. flavus (Dorner, J. W. 2004. J. Toxicol.—Toxin Rev. 23: 425-450). Brown et al. (1991. J. Food Protect. 54: 623-626) demonstrated that aflatoxin levels could be suppressed by direct wounding and injection of corn ears with a non-toxigenic strain of A. flavus. In contrast to the direct, mechanical delivery strategy of Brown et al., an indirect delivery to soil is more routinely used. Here, the soil inoculum is typically an aggressive, non-toxigenic strain of A. flavus, which is initially cultured on cereal grains. These grains serve as a nutrient source for proliferation of the biocontrol A. flavus strain and are applied as soil treatments to target crops. While on the grains, the non-toxigenic strain sporulates profusely, disperses by wind or water, and competes with endemic aflatoxigenic strains for resources, collectively resulting in a reduction of aflatoxin levels. This soil treatment strategy has been successful in peanuts (Dorner et al. 1992. J. Food Protect. 55: 888-892), cotton (Cotty, P. J. 1994. Phytopath. 84: 1270-1277) and corn (Dorner et al. 1999. J. Food Protection 62: 650-656). A similar strategy using a soil-applied inoculation was implemented for Mississippi Delta corn production (Abbas et al. 2006. Biocontrol Sci. Tech. 16: 437-449). The Mississippi Delta corn study identified K49, a non-toxigenic strain of A. flavus that exhibited both significant reduction of aflatoxin contamination in four years of field trials and good colonization potential.
Despite the success of the above treatment strategies, there are associated limitations in reduction to practice in a commercial agricultural setting. Consequently, there remains a need to develop a direct aerial delivery approach to effectively mitigate aflatoxin contamination in preharvest corn and to alleviate application dependency on optimal environmental conditions.